A cup brush on a small grinder can help too. If you clean up the threads before you go after the nuts, you have less chance that it will start going and then seize up again a little farther down. Down here in the swamp, galvanized will fail pretty fast too so these things tend to get painted.
This is the sort of thing you want to do in the "staging" step so you don't have a crew and a crane operator twiddling their thumbs while you are fighting rusty hardware.
It might be worth running every one out and back in one at a time before you start for real.
An impact wrench is great for that part. I have an 18v Makita that will beat my pneumatic I/R gun.
